The present invention relates to cement. More particularly, the present invention relates to a slag cement mixture and a process of making the same. While the invention is subject to a wide range of applications, it is especially suited for use in structural concrete and concrete construction.
Cement is a widely used building material. A particularly popular variety of cement is portland cement. Portland cement is used in many applications such as mortar, concrete, and cement building materials such as building blocks. Portland cement is produced by pulverizing clinker to a specific surface area of about 3,000 to 5,000 cm2/g or finer. Clinker is created in a cement kiln at elevated temperatures from ingredients such as limestone, shale, sand, clay, and fly ash. The cement kiln dehydrates and calcines the raw materials, and produces a clinker composition comprised of tricalcium silicate (3CaOxe2x80x94SiO2), dicalcium silicate (2CaOxe2x80x94SiO2), tricalcium aluminate (3CaOxe2x80x94Al2O3), and tetracalcium aluminoferrite (4CaOxe2x80x94Al2O3xe2x80x94Fe2O3).
Conventional mortar and concrete compositions contain cement, aggregates such as gravel and sand, and water to activate the hydration process. A mortar product is a hardened cement product obtained by mixing cement, a fine aggregate, and water. A concrete product is a hardened cement product obtained by mixing cement, coarse aggregate, water, and often a fine aggregate as well.
The strength properties of concrete and mortar products depend in part on the relative proportions of cement, aggregates, and water. The American Society for Testing and Materials (xe2x80x9cASTMxe2x80x9d) standard test procedures, such as ASTM C192 and C39 describe the procedures for mixing, casting, curing, and testing portland cement concrete mixtures with 1, 3, 7, 14, and 28 day standards. Greater compressive strength is a desirable feature of cement, and a number of materials have been used to improve the compressive strength of cements.
One way of improving the compressive strength of hardened cement is to blend ground granulated blast furnace slag with cement to give an improved cement composition. Blast furnace slag is a by-product of the production of iron in a blast furnace consisting of silicates and aluminosilicates of calcium. A quick setting cement can be produced by grinding blast furnace slag with gypsum. (See, for example, U.S. Pat. Nos. 1,627,237 and 2,947,643). Blast furnace slag has hydraulic properties very similar to portland cement, and adding blast furnace slag to cement is routine to increase the cement""s strength. (See ASTM Specification C989).
Typical North American blast furnace slag composition ranges are 32-40% SiO2, 7-17% Al2O3, 29-42% CaO, 8-19% MgO, 0.7-2.2% SO3, 0.1-1.5% Fe2O3, and 0.2-1.0% MnO. (see The Portland Cement Association Research and Development Bulletin RD112T). Blast furnaces in the U.S. are operated using a basic slag, typically defined as the slag ratio: (% CaO+% MgO)/(% SiO2 +% Al2O3), where the slag ratio is maintained in excess of 1.0 in order to remove sulfur from the iron produced and to facilitate producing an iron of high carbon content. The chemical composition of blast furnace slag also varies world wide, especially in alumina content. Blast furnace slags have long been recognized as very useful commodities and have been used in a number of applications. In addition to its use as cement additive, blast furnace slag has been used in asphalt, sewage trickle-filter media, roadway fills, and railroad ballast.
Blast furnace slags can be used to prevent excessive expansion of concrete mixtures that have a high-alkali content and aggregates that are alkali-reactive. Use of blast furnace slag as 40% or more of such a cement mixture can prevent excessive expansion. Blast furnace slag is characterized by its short setting time, which is the time between the addition of mixing water to a cementitious mixture and when the mixture reaches a specified degree of rigidity as measured by a specified procedure.
Steel slag is also used as a cement additive. Steel slag is formed in the process of making steel in a blast furnace, and often has a high concentration of ferrites. Because of its high ferrite composition, steel slag is generally used as a filler in cement road building material or as a feedstock raw material in cement kilns. It is possible to produce a hydraulic cement base from steel slag by adding further minerals to the slag portion, thereby reducing the ferrite composition of the slag. This additional step, while rendering a usable product, is costly and time consuming.
Mixtures of blast furnace slag and steel slag have resulted in stronger cement products, but cupola furnace slag, a by-product of cast iron production, is only rarely used in cement except as a processing addition. (See ASTM C465 and Cupola Handbook, published by the American Foundrymen""s Society). Blast furnaces and cupola furnaces are operated differently and are used to make different iron products, consequently, the slag products of these furnaces are also different, both in chemical composition and in material properties. Cupola slag has different hydraulic properties than blast furnace slag. For example, cupola slag blended cement sets more slowly and at 7 days lacks the strength of blast furnace slag blended cements. Also, cupola slag is not a common concrete additive due to environmental concerns such as the possibility of rain water leaching out some of its components. Indeed, cupola slag often presents a disposal problem, which creates an additional expense, ultimately increasing the cost of the iron produced.
There is an ever present need in the cement art for harder, stronger cement products with longer setting times. There is also a need in the cast-iron production art for a disposal method for cupola slag that is environmentally safe and economically practical.
Accordingly, the present invention is directed to a cupola slag blended cement with an increased compressive strength. The principal advantage of the present invention is a cement mixture that results in a concrete which is both harder and stronger while providing a means of recycling cupola slag that is both environmentally sound and economically practical. The cement compositions of the present invention have a resistance to expansion due to sulfate attack and alkali silica reaction, and can be formulated to have a wide range of curing times.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention is a hydraulic cement containing cupola slag ground to a fineness of greater than 4,000 cm2/g blended with portland cement. A preferred embodiment of the invention is a hydraulic cement containing cupola slag ground to a fineness of greater than 5,000 cm2/g blended with portland cement. In the most preferred embodiment, the invention is a hydraulic cement containing cupola slag ground to a fineness of between 6,000 cm2/g and 7,000 cm2/g.
In one embodiment, the invention is a hydraulic cement containing from about 20 to 50% of a ground granulated cupola furnace slag blended with portland cement. In a preferred embodiment, the invention is a hydraulic cement containing from about 30% to 40% cupola slag blended with portland cement. In another preferred embodiment, the invention is a hydraulic cement containing about 35% cupola slag blended with portland cement.
The invention includes ground granulated cupola furnace slag with a fineness of about 5,000 to about 7,000 cm2/g and meeting the fineness requirement of the ASTM C989 Grade 100 specification for blast furnace slag.
The invention includes ground granulated cupola furnace slag with a fineness of about 6,000 to about 6,750 cm2/g. The invention also includes ground granulated cupola furnace slag with a fineness of about 6,500 cm2/g.
In one embodiment of the invention, a blended cement mixture of about 35% cupola furnace slag displays a 28 day compressive strength of more than 7,000 psi and a flexural strength of more than 700 psi.
In another embodiment of the invention, the total heat of hydration of the blended cement mixture of about 35% cupola furnace slag does not exceed 250 J/g when measured for 72 hours, and the expansion of mortar bars does not exceed 0.20% at when measured at 14 days.
In one embodiment, the invention includes a process of using cupola slag as a raw cement kiln feedstock.